The briquetting of particulate materials has been carried out for many years. Typically, materials such as charcoal were compacted by briquetting apparatus at relatively low pressures and temperatures. In recent years, briquetting techniques have been applied to compact other materials such as particulate metals and ceramic materials. Briquetting of such materials requires the use of high temperatures and pressures.
The use of high pressures between the briquetting rolls, the maintenance of high pressures at elevated temperatures as well as the abrasive nature of many of the materials compacted to form briquets results in a serious wear problem. Because of the nature of the wear problem, briquetting apparatus normally includes rolls having replaceable mold segments. Briquetting rolls having replaceable mold segments, have by their economies of operation, received substantial commercial acceptance for the compaction of particulate materials at high temperatures and pressures. Such economies, however, depend in part upon the frequency of replacement of the mold segments.
The materials used for the construction of the mold segments must exhibit very high strengths due to their exposure to high temperature and pressure. Because of the nature of the materials used for construction of the mold segments, when they have sufficient strength they are also quite brittle and incapable of tolerating significant distortion before they fracture.
It is one object of the present invention to provide a configuration for the mold segment, and the cavity within which the mold segment is affixed to the cylindrical roll, that reduces the bending and tension forces on the mold segments. The mold segments formed of these strong but brittle materials exhibit significantly longer useful lives by the elimination of such forces.
In addition to minimizing such forces on the mold segments, the configuration of the mold segments and the cylindrical member comprising the briquetting roll also must conform to the requirements of commercially viable briquetting rolls. The segments must be readily replaceable, relatively easy to manufacture without reliance on extremely close tolerances to effect the desired structure of the briquetting roll.
A number of briquetting roll structures incorporating replaceable mold segments are known in the art. For various reasons, none of these mold segments or briquetting rolls are completely satisfactory for use with briquetting operations using strong, but brittle materials for the mold segments.
One such type of briquetting roll assembly having replaceable mold segments is depicted in U.S. Pat. No. 3,907,485. The briquetting roll disclosed in this patent comprises a cylindrical central member adapted to receive a plurality of mold segments in its periphery. The mold segments are affixed to the cylindrical central member by fasteners engaging projections extending outwardly from the sidewalls of the mold segment. The configuration of the mold segment in its cooperation with the central member are such that radial compression forces applied to the mold segment are transmitted through the bottom surface of the mold segment which are coplanar with the projections from the sidewalls. The application of such forces to the mold segments produces bending stresses in the mold segment that can result in premature failure due to cracking of the strong, but brittle mold segment.
U.S. Pat. No. 3,077,634 discloses a type of briquetting roll structure with replaceable mold segments wherein the radial pressure applied to the mold segment is transmitted to the cylindrical central member through bottom surface of the mold segment. While the configuration of the mold segment would appear to reduce the bending stresses applied to the mold segment, the means of affixing the mold segment to the central member has several disadvantages. To obtain rigid clamping of the mold segments onto the cylindrical central member, each of the segments must be precisely machined so that they are the same length. If one mold segment is longer than another, it prevents the retaining rings that engage the sidewalls of the mold segments from being drawn tightly about all of the mold segments. This results in a lack of lateral restraint for other mold segments during the briquetting operation. The movement of the mold segments during the briquetting operation damages the cylindrical central member as well as causing damage to the mold segments themselves.
U.S. Pat. No. 3,690,062 discloses a segmented briquetting roll wherein the radial stress applied to the mold segment is transmitted to the cylindrical control member through the angularly disposed lower surface of the mold segments. The means of affixing the mold segments to the central member includes segment configurations that can cause localized bending at high stresses leading to the possibility of premature mold segment failure at the affixing means.
The briquetting roll structure of the present invention with the novel mold segment provides a detachable mold segment that can be readily manufactured, easily replaced in a briquetting roll structure. Furthermore, such a mold segment is not susceptible to breakage due to localized stresses or bending of the mold segment when it is subjected to the high pressures developed in modern briquetting operations.
The primary object of the present invention is to provide a readily manufactured, replaceable mold segment useful in briquetting operations having an enhanced service life due to the radial pressures of the briquetting operation being applied to the central member by the mold segments substantially through the sidewalls of the mold segments.
Other objects of the invention will be apparent from the following detailed description of the preferred embodiments or can be learned through practice of the invention as it is disclosed.